Cables with a halogen-free recyclable coating comprising polypropylene and an ethylene copolymer having high structural uniformity

ABSTRACT

A cable, in particular for power transmission, for telecommunications or for data transmission, or also combined power/telecommunications cables, wherein at least one coating layer consists of a recyclable material which is halogen-free and has superior mechanical and electrical properties. This material consists of a polymer mixture comprising: (a) a crystalline propylene homopolymer or copolymer; and (b) a copolymer of ethylene with at least one alpha-olefin having from 4 to 12 carbon atoms, and optionally with a diene; the said copolymer (b) being characterized by a density of between 0.90 and 0.86 g/cm 3  and by a Composition Distribution Index, defined as the weight percentage of copolymer molecules having an alpha-olefin content within 50% of the average total molar content of alpha-olefin, of greater than 45%.

CROSS-REFERENCES TO RELATED APPLICATIONS

Applicant claims the right of priority under 35 U.S.C. § 119(a)-(d)based on patent application No. MI97A 001739, filed Jul. 23, 1997, inItaly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to cables, in particular for powertransmission, for telecommunications or for data transmission, or alsocombined power/telecommunications cables, wherein at least one coatinglayer consists of a recyclable material which is halogen-free and hassuperior mechanical and electrical properties.

2. Description of the Related Art

There is currently a great need for highly environmentally friendlyproducts, consisting of materials which are not harmful to theenvironment either during their production or when in use, and which arereadily recyclable at the end of their working life. However, the optionof using ecological materials is, in all cases, subject to the need tokeep costs within acceptable limits, while still guaranteeingperformances which are at least equivalent to those of conventionalmaterials and which are, in any case, satisfactory under the most commonconditions of use.

In the cables sector, in particular power transmission cables, thevarious coatings surrounding the conductor commonly consist ofcrosslinked polymer materials, in particular polyethylene or ethylenecopolymers suitably crosslinked during extrusion, so as to givesatisfactory mechanical performances even under heating in continuoususe and under conditions of current overload, while at the same timemaintaining a high level of flexibility. These materials are crosslinkedand therefore cannot be recycled since they are devoid of thermoplasticproperties, hence they can only be disposed of at the end of theirworking life by means of incineration. Moreover, in certain cases theouter protective sheath consists of polyvinyl chloride (PVC) which isdifficult to separate by conventional methods (for example in water bydensity differences) from the crosslinked polyolefins containinginorganic fillers (for example from ethylene/propylene rubberscontaining inorganic fillers), and, on the other hand, PVC cannot beincinerated together with crosslinked polyolefins since this produceshighly toxic chlorinated products by combustion.

In U.S. Pat. No. 4,948,669 cable-coating compositions are describedcomprising from 29 to 50% by weight of low-density polyethylene,containing as comonomer an alpha-olefin having from 4 to 12 carbonatoms, in particular 1-octene, in an amount such as to obtain a densityof between 0.90 and 0.92 g/cm³, in admixture with: (a) a propylenehomopolymer; (b) a non-elastomeric copolymer of propylene with ethylene;or (c) heterogeneous copolymers of propylene with ethylene, obtained inreactor. As polyethylene it is particularly suggested using productDowlex® 4000E from Dow Chemical, containing about 17% of 1-octene andhaving a melt index equal to 3.3 and a density of 0.912 g/cm³. These areproducts obtained using titanium-based Ziegler-Natta catalysts, having arelatively high density and thus little flexibility.

In patent application WO 96/23311 a low-voltage high-current cable isdescribed, wherein the insulating coating, the inner sheath and theouter sheath are made of the same non-crosslinked polymer-based materialwhich is black coloured by addition of carbon black. Using the same basematerial would allow recycling without the need to separate differentmaterials. As polymer material for the outer sheath, it is suggestedusing, in place of PVC, ultra-low-density polyethylene (ULD-PE), forexample products Engage® from DuPont-Dow Elastomers and Exxpol® fromExxon. Inorganic fillers such as aluminium or magnesium hydroxide areadded to these materials in order to give them flame-retardantproperties.

In U.S. Pat. No 5,246,783 cables are described, having as insulatingand/or semiconductive coatings polymer materials based on copolymers ofethylene with at least one C₃-C₂₀ alpha-olefin, with a density of from0.86 to 0.96 g/cm³, known commercially under the tradename Exact® fromExxon, preparable using metallocene catalysts. These copolymers are usedin crosslinked form, achieved by chemical means (for example withdicumyl peroxide) or by irradiation.

BRIEF DESCRIPTION SUMMARY OF THE INVENTION

The Applicant has perceived that the technical problem of obtaining acable with a coating made of a non-crosslinked, and thus recyclable,polymer material which also has mechanical and electrical propertiessuitable to the usual conditions of use is dependent on the use of acrystalline propylene homopolymer or copolymer mixed with a copolymer ofethylene with an alpha-olefin having a low density and a high structuraluniformity, in particular having a highly homogeneous distribution ofthe alpha-olefin between the polymer molecules. This high structuraluniformity is obtainable in particular by copolymerization of thecorresponding monomers in the presence of a single-site catalyst, forexample a metallocene catalyst.

In particular, the Applicant has found that excellent performances, bothin terms of mechanical properties, in particular elongation at break,stress at break and modulus, and in terms of electrical properties, maybe obtained by using, as non-crosslinked base material for at least oneof the coating layers of the cable, a mixture as defined hereinbelow,comprising polypropylene and a copolymer of ethylene with at least oneC₄-C₁₂ alpha-olefin and optionally with a diene comonomer, having adensity of from 0.90 to 0.86 g/cm³ and a Composition Distribution Index,defined as the weight percentage of copolymer molecules having analpha-olefin content within 50% of the average total molar content ofalpha-olefin, of greater than 45%.

Therefore, according to a first aspect, the invention relates to a cablecomprising a conductor and one or more coating layers, wherein at leastone of the said coating layers comprises, as non-crosslinked basepolymer material, a mixture comprising: (a) a crystalline propylenehomopolymer or copolymer; and (b) a copolymer of ethylene with at leastone alpha-olefin having from 4 to 12 carbon atoms, and optionally with adiene; the said copolymer (b) being characterized by a density of from0.90 to 0.86 g/cm³ and a Composition Distribution Index, defined as theweight percentage of copolymer molecules having an alpha-olefin contentwithin 50% of the average total molar content of alpha-olefin, ofgreater than 45%.

According to a further aspect, the invention relates to a cablecomprising a conductor and one or more coating layers, wherein at leastone of the said coating layers has electrical insulating properties andcomprises a mixture as defined above as non-crosslinked base polymermaterial.

According to a further aspect, the invention relates to a cablecomprising a conductor and one or more coating layers, wherein at leastone of the said coating layers has semiconductive properties andcomprises a mixture as defined above as non-crosslinked base polymermaterial.

According to a further aspect, the invention relates to a cablecomprising a conductor and one or more coating layers, wherein at leastone of the said coating layers is an outer protective sheath andcomprises a mixture as defined above as non-crosslinked base polymermaterial.

According to a further aspect, the invention relates to a cablecomprising a conductor and one or more coating layers, wherein at least70%, preferably at least 90%, by weight relative to the total weight ofthe base polymer material of the said coating layers consists of themixture as defined above.

The Composition Distribution Index provides a measure of thedistribution of the alpha-olefin between the copolymer molecules (thehigher the value of this index, the more homogeneous is the distributionof the comonomer between the copolymer molecules) and can be determinedby techniques of Temperature Rising Elution Fractionation, as described,for example, in patent U.S. Pat. No. 5,008,204 or in Wild et al., J.Poly. Sci. Poly. Phys. Ed., Vol. 20, p.441 (1982).

The copolymers (b) have a molecular weight distribution index, definedas the ratio between the weight-average molecular weight M_(W), and thenumber-average molecular weight M_(n), which is generally low, usuallybetween 1.5 and 3.5. The molecular weight distribution index can bedetermined by conventional methods, by means of Gel PermeationChromatography (GPC).

The copolymers (b) are also generally characterized by a meltingenthalpy of from 30 to 60 J/g.

Copolymers of ethylene with at least one C₄-C₁₂ alpha-olefin, andoptionally with a diene, having these characteristics are obtainable bycopolymerization of ethylene with the alpha-olefin, and optionally withthe diene comonomer, in the presence of a single-site catalyst, forexample a metallocene catalyst, as described, for example, in U.S. Pat.Nos. 5,246,783 and 5,272,236, or alternatively they may be obtainedcommercially under the trademarks Engage® from DuPont-Dow Elastomers andExact® from Exxon Chemical. The metallocenes used to polymerize theolefins are coordination complexes of a transition metal, usually fromGroup IV, in particular titanium, zirconium or hafnium, with twooptionally substituted cyclopentadienyl ligands, used in combinationwith a co-catalyst, for example an alumoxane, preferablymethylalumoxane, or a boron compound (see for example J. M. S.-Rev.Macromol. Chem. Phys., C34(3), 439-514 (1994); J. OrganometallicChemistry, 479 (1994), 1-29, or alternatively patents U.S. Pat. Nos.5,414,040, 5,229,478, WO 93/19107 and EP-A-632,065, or the alreadymentioned U.S. Pat. Nos. 5,246,783 and 5,272,236). Catalysts which aresuitable for obtaining the copolymers (b) according to the presentinvention are also the so-called Constrained Geometry Catalystsdescribed, for example, in patents EP-416,815 and EP-418,044.

With the term alpha-olefin it is meant an olefin of formula CH₂═CH—R,where R is a linear or branched alkyl having from 2 to 10 carbon atoms.The alpha-olefin may be selected, for example, from 1-butene, 1-pentene,4-methyl-1-pentene, 1-hexene, 1-octene, 1-dodecene and the like.1-hexene and 1-octene are particularly preferred.

When a diene termonomer is present, this generally has from 4 to 20carbon atoms, and is preferably selected from: linear, conjugated ornon-conjugated diolefins, for example 1,3-butadiene, 1,4-hexadiene or1,6-octadiene; monocyclic or polycyclic dienes, for example1,4-cyclohexadiene, 5-ethylidene-2-norbornene, 5-methylene-2-norborneneand the like.

Ethylene/alpha-olefin or ethylene/alpha-olefin/diene copolymers whichcan be used according to the present invention generally have thefollowing composition: 75-97 mol %, preferably 90-95 mol %, of ethylene;3-25 mol %, preferably 5-10 mol %, of alpha-olefin; 0-5 mol %,preferably 0-2 mol %, of a diene.

The crystalline propylene homopolymer or copolymer (a) generally has amelting enthalpy of greater than 75 J/g, preferably greater than 85 J/g.It may be selected in particular from:

(1) isotactic propylene homopolymers with an isotactic index of greaterthan 80, preferably greater than 90, even more preferably greater than95;

(2) propylene homopolymers obtainable using metallocene catalysts,having a pentad mmmm content of greater than 90% (determined by ¹³C-NMRanalysis);

(3) crystalline copolymers of propylene with ethylene and/or analpha-olefin having from 4 to 10 carbon atoms, with an overall contentof ethylene and/or alpha-olefin of less than 10 mol %;

(4) heterogeneous propylene copolymers obtainable by blockpolymerization of propylene and of mixtures of propylene with ethyleneand/or an alpha-olefin having from 4 to 10 carbon atoms, containing atleast 70% by weight of polypropylene homopolymer or of crystallinepropylene/ethylene copolymer, with an isotactic index of greater than80, the remainder consisting of an elastomeric ethylene/propylenecopolymer with a propylene content of from 30 to 70% by weight;

(5) crystalline propylene homopolymers or copolymers of syndiotacticstructure, obtainable using metallocene catalysts.

According to the present invention, the ethylene/alpha-olefin orethylene/alpha-olefin/diene copolymer (b) as described above is presentin admixture with the crystalline propylene homopolymer or copolymer (a)in a predetermined amount, such as to make the resulting polymer mixturesufficiently flexible, and in particular so as to give it a elongationat break value, measured according to CEI standard 20-34, §5.1, of atleast 100%, preferably of at least 200%, and a 20% modulus value,measured according to CEI standard 20-34, §5.1, of less than 10 MPa,preferably less than 7 MPa.

In general, these characteristics are obtainable using mixturescomprising from 10 to 60%, preferably from 15 to 50%, by weight ofcrystalline propylene homopolymer or copolymer (a) and from 40 to 90%,preferably from 50 to 85%, by weight of ethylene/alpha-olefin orethylene/alpha-olefin/diene copolymer (b), the percentages beingrelative to the total weight of the polymeric components (a) and (b).

In accordance with the present invention, the use of non-crosslinkedpolymer mixtures as defined above makes it possible to obtain arecyclable, flexible coating which has excellent mechanical properties,both in terms of modulus and in terms of elongation and stress at break.In particular, it is possible to obtain mechanical performances underheating, that is at 90° C. for continuous use and at 130° C. in the caseof current overload, which are comparable with the typical performancesof the polyethylene-based crosslinked coatings currently on sale, makingthe above-mentioned mixtures suitable not only for low voltage but alsofor medium- and high-voltage cables.

The mechanical properties mentioned above are accompanied by excellentelectrical properties, such as insulation constant (Ki) and dielectricloss (tan delta), both under dry conditions and when the cable issubmerged in water. In particular, it has been found that thenon-crosslinked material according to the present invention has a veryhigh insulation constant which is maintained within acceptable valueseven after prolonged immersion in water.

The fact that an insulating material has low water absorption makes itpossible to reduce dielectric loss remarkably and thus to achieve lowerenergy dissipation levels, in particular during high power transmission.In the case of low-voltage high-current power transmission, low waterabsorption avoids an excessive reduction of electrical resistivity ofthe insulating material and thus of its electrical performance.

The polymer mixtures according to the present invention are also capableof containing inorganic fillers without an unacceptable reduction intheir mechanical and elastic properties, in particular as to elongationat break, which remains well above 100%. It is thus possible to producecompositions with flame-retardant properties which are endowed with highflexibility and high mechanical strength.

Thus, according to a further aspect, the present invention relates to aflame-retardant polymer composition, comprising:

(a) a crystalline propylene homopolymer or copolymer;

(b) a copolymer of ethylene with at least one alpha-olefin having from 4to 12 carbon atoms, and optionally with a diene; the said copolymer (b)being characterized by a density of between 0.90 and 0.86 g/cm³ and by aComposition Distribution Index, defined as the weight percentage ofcopolymer molecules having an alpha-olefin content within 50% of theaverage total molar content of alpha-olefin, of greater than 45%;

(c) an inorganic filler in an amount such as to impart flame-retardantproperties.

Moreover, a further aspect of the present invention resides in a cablecomprising a conductor and one or more coating layers, wherein at leastone of the said coating layers comprises a flame-retardant polymercomposition as defined above.

The inorganic filler is generally an inorganic oxide, preferably inhydrate or hydroxide form. Examples of suitable compounds are aluminium,bismuth, cobalt, iron, magnesium, titanium or zinc oxides and thecorresponding hydroxides, or mixtures thereof. Magnesium hydroxide,aluminium hydroxide and alumina trihydrate (Al₂O₃.3H₂O) or mixturesthereof are particularly preferred. One or more inorganic oxides orsalts such as CoO, TiO₂, Sb₂O₃, ZnO, Fe₂O₃, CaCO₃ or mixtures thereofmay advantageously be added to these compounds in minor amounts,generally less than 25% by weight. Preferably, the above-mentioned metalhydroxides, in particular magnesium and aluminium hydroxides, are usedin the form of particles having sizes which can range from 0.1 to 100μm, preferably from 0.5 to 10 μm. In the case of hydroxides, these mayadvantageously be used in the form of coated particles. Saturated orunsaturated fatty acids containing from 8 to 24 carbon atoms, and metalsalts thereof, are usually used as coating materials, such as, forexample: oleic acid, palmitic acid, stearic acid, isostearic acid,lauric acid; magnesium or zinc stearate or oleate; and the like.

The amount of inorganic filler which is suitable for impartingflame-retardant properties may vary within a wide range, generallybetween 10 and 80% by weight, preferably between 30 and 70% by weight,with respect to the total weight of the composition.

A coupling agent selected from those known in the art, for examplesilane compounds or carboxylic derivatives having at least one ethylenicunsaturation can be added to the mixture in order to enhance thecompatibility between the inorganic filler and the polymer matrix.

Examples of silane compounds which are suitable for this purpose are:γ-methacryloxypropyltrimethoxysilane, methyltriethoxysilane,methyltris(2-methoxy ethoxy)silane, dimethyldiethoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltrimethoxysilane, vinyl triethoxysilane,octyltriethoxysilane, isobutyl triethoxysilane, isobutyltrimethoxysilaneand mixtures thereof.

Carboxylic derivatives with ethylenic unsaturation which mayadvantageously be used as coupling agents are, for example, unsaturatedcarboxylic anhydrides or, preferably, unsaturated dicarboxylicanhydrides; maleic anhydride is particularly preferred. Alternatively,it is possible to use polyolefins as compatibilizing agents, thesepolyolefins optionally containing ethylenic unsaturations, on whichcarboxylic groups have been grafted by reaction with the above-mentionedcarboxylic derivatives having at least one ethylenic unsaturation.

The coupling agent, either of silane type or of carboxylic type, can beused in its normal state or can be grafted to at least one of thepolymer components of the mixture.

The amount of coupling agent to be added to the mixture may vary mainlydepending on the type of coupling agent used and on the amount ofinorganic filler added, and is generally between 0.05 and 30%,preferably between 0.1 and 20%, by weight, relative to the total weightof the base polymer mixture.

Other conventional components such as antioxidants, fillers, processingco-adjuvants, lubricants, pigments, water-tree retardant additives andthe like are usually added to the base polymer material. In the case ofthe semiconductive layers 3 and 5, the polymer material is preferablyfilled with carbon black in an amount such as to give this materialsemiconductive properties (namely, so as to obtain a resistivity of lessthan 5 ohm.m at room temperature).

Suitable conventional antioxidants are, for example: polymerizedtrimethyldihydroquinoline, 4,4′-thiobis(3-methyl-6-tert-butyl)phenol;pentaerythryl-tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],2,2′-thiodiethylene-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]and the like, or mixtures thereof.

Other fillers which may be used in the present invention include, forexample, glass particles, glass fibres, calcined kaolin, talc and thelike, or mixtures thereof. Processing co-adjuvants usually added to thepolymer base are, for example, calcium stearate, zinc stearate, stearicacid, paraffin wax and the like, or mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details will be illustrated in the following detaileddescription, with reference to the appended drawing, wherein:

FIG. 1 is a perspective view of an electrical cable, particularlysuitable for medium voltages, according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, the electrical cable 1 comprises a conductor 2; an innerlayer 3 with semiconductive properties; an intermediate layer 4 withinsulating 5 properties; an outer layer 5 with semiconductiveproperties; a screen 6; and an outer sheath 7.

The conductor 2 generally consists of metal wires, preferably made ofcopper or aluminium, which are braided together using conventionaltechinques.

At least one of the layers 3, 4 and 5, and preferably at least theinsulating layer 4, comprises polypropylene as non-crosslinked basepolymer material, mixed with a copolymer of ethylene with at least onealpha-olefin, and optionally with a diene, as defined above. In apreferred embodiment of the present invention, all of the insulating andsemiconductive layers 3, 4 and 5 comprise a polymer mixture as definedabove as non-crosslinked base polymer material.

A screen 6, generally consisting of helically wound electricallyconductive wires or strips, is usually placed around the outersemiconductive layer 5. This screen is then covered with a sheath 7,consisting of a thermoplastic material such as polyvinyl chloride (PVC),non-crosslinked polyethylene (PE) or, preferably, a mixture comprisingpolypropylene and an ethylene/alpha-olefin orethylene/alpha-olefin/diene copolymer, as defined above.

FIG. 1 shows only one possible embodiment of a cable according to thepresent invention. It is clear that suitable changes known in the artmay be made to this embodiment without thereby departing from the scopeof the present invention. In particular, the recyclable polymer mixturesaccording to the present invention may advantageously also be used forcoating telecommunications cables or data transmission cables, oralternatively combined power/telecommunications cables.

The properties of the polymer materials used according to the presentinvention (Cop. 1 and 2) and of the material used for comparativepurposes (Cop. 3) are given in Table 1. As melting enthalpy the secondmelting value (ΔH_(2m)) is given, obtained by DSC at a scan speed of 10°C./min. The melt flow index (MFI) was measured according to ASTMstandard D 1238/L (at 230° C. and 21.6 N for polypropylene, and at 190°C. and 21.6 N for ethylene/1-octene copolymers). The CompositionDistribution Index (CDI) was determined by Temperature Rising ElutionFractionation techniques.

TABLE 1 Polymer Density MFI CDI ΔH_(2m) material (g/cm³) (dg/min) (%)(J/g) PP 1 0.900 1.6 — 98 PP 2 0.900 1.8 — 90 Cop. 1 0.885 1.0 >70 55.6Cop. 2 0.868 0.5 >70 34.4 Cop. 3 0.902 3.0 — 78.0

PP 1 (Moplen® S30G—Montell): isotactic poly propylene (homopolymer);

PP 2 (Moplen® EP2S30B—Montell): random crystalline propylene/ethylenecopolymer;

Cop. 1 (Engage® 8003—DuPont-Dow Elastomers): ethylene/1-octene copolymerwith 82/18 weight ratio (5.5 mol % of 1-octene), obtained by metallocenecatalysis;

Cop. 2 (Engage® 8150—DuPont-Dow Elastomers): ethylene/1-octene copolymerwith 75/25 weight ratio (7.6 mol % of 1-octene), obtained by metallocenecatalysis;

Cop. 3 (Stamylex® TMX 1000—DSM): ethylene/1-octene copolymer (4.6 mol %of 1-octene), obtained using a titanium Ziegler-Natta catalyst.

The polymer materials in Table 1 were used to prepare the mixtures givenin Table 2.

The mixtures 1-3 a were prepared in a Brabender mixer (volume of themixing chamber: 80 cm³), filled to 95% of volume. Mixing was carried outat a temperature of 170° C. for a total time of 10 min (rotor speed: 40rpm). At the end of the mixing, the final torque (reported in Table 2)was measured under the abovementioned conditions.

Mixtures 4, 5 and 6 were prepared in a 20 mm-diameter counter-rotatoryBrabender twin-screw mixer with a rotor speed of 50 rpm and with thefollowing temperature profile: 1st zone=100° C., 2nd zone=160° C., 3rdzone=190° C., 4th zone=190° C.

For the filled systems there were used:

Hydrofy® GS-1.5: Mg(OH)₂ coated with stearic acid from SIMA (averageparticle diameter: 2 μm; specific surface: 11 m²/g);

Rhodorsil® MF175U: silicone rubber from Rhône-Poulenc acting asprocessing co-adjuvant/lubricant.

The following were used as antioxidants:

Irganox® 1010: pentaerythritoltetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Ciba-Geigy);

Irganox® PS802 FL: distearyl thiodipropionate (DSTDP) (Ciba-Geigy).

The compositions are given in Table 2 as phr (i.e. parts by weight per100 parts of polymer matrix).

The mixtures thus obtained were subjected to mechanical tensile strengthtests according to CEI standard 20-34, §5.1, on test specimens obtainedfrom 1 mm-thick plates obtained by compression moulding at 190-195° C.and 200 bar after preheating for 5 min at the same temperature. Thepulling speed of the clamps was 250 mm/min for mixtures 1 -3a, and 50mm/min for mixtures 4, 5 and 6. The results are given in Table 2.

TABLE 2 EXAMPLE 1 1a 2 2a 3(*) 3a(*) 4 5 6(*) PP 1 — — — — — — 40 40 40PP 2 35 35 35 35 35 35 — — — Cop. 1 65 65 — — — — 60 — — Cop. 2 — — 6565 — — — 60 — Cop. 3 — — — — 65 65 — — 60 Hydrofy ® GS-1.5 — 160 — 160 —160 — — — Rhodorsil ® MF175U — 1.5 — 1.5 — 1.5 — — — Irganox ® PS 802FL— — — — — — 0.2 0.2 0.2 Irganox ® 1010 — 0.5 — 0.5 — 0.5 0.1 0.1 0.1Final torque (N · m) 6.2 9.8 7.8 11.2 6.1 7.3 — — — Stress at break(MPa) 16.7 10.5 17.5 10.4 6.9 5.5 15.1 20.4 9.1 Elongation at break (%)662 567 713 621 711 54 702 695 33 10% modulus (MPa) — — — — — — 4.1 4.58.3 20% modulus (MPa) 6.0 5.6 4.8 4.7 8.0 6.6 — — — (*)comparative

What is claimed is:
 1. A cable comprising a conductor and one or morecoating layers, wherein at least one of-the coating layers comprises, asnon-crosslinked base polymer material, a mixture comprising: (a) acrystalline propylene homopolymer or copolymer; and (b) a copolymer ofethylene with at least one alpha-olefin having from 4 to 12 carbonatoms, and optionally, a diene; the copolymer (b) characterized by adensity between and 0.86 g/cm³ and 0.90 g/cm³, and by a CompositionDistribution Index, defined as the weight percentage of copolymermolecules having an alpha-olefin content within 50% of the average totalmolar content of alpha-olefin, of greater than 45%.
 2. The cable ofclaim 1, wherein at least one of the coating layers has electricalinsulating properties and comprises a mixture of (a) and (b) asnon-crosslinked base polymer material.
 3. The cable of claim 1, whereinat least one of the coating layers has semiconductive properties andcomprises a mixture of (a) and (b) as non-crosslinked base polymermaterial.
 4. The cable of claim 1, wherein at least one of the coatinglayers is an outer protective sheath and comprises a mixture of (a) and(b) as non-crosslinked base polymer material.
 5. The cable of claim 1,wherein at least 70%, preferably at least 90%, by weight relative to thetotal weight of the base polymer material of the coating layers consistsof a mixture of (a) and (b).
 6. The cable of claim 1, wherein thecopolymer (b) has a molecular weight distribution index of between 1.5and 3.5.
 7. The cable of claim 1, wherein the copolymer (b) has amelting enthalpy between 30 J/g and 60 J/g.
 8. The cable of claim 1,wherein the copolymer (b) is obtainable by copolymerization of ethylenewith an alpha-olefin, and optionally, a diene, in the presence of asingle-site catalyst.
 9. The cable of claim 8, wherein the single-sitecatalyst is a metallocene catalyst.
 10. The cable of claim 8, whereinthe single-site catalyst is a Constrained Geometry Catalyst.
 11. Thecable of claim 1, wherein the copolymer (b) comprises: 75-97 mol % ofethylene; 3-25 mol % of alpha-olefin; and 0-5 mol % of a diene.
 12. Thecable of claim 11, wherein the copolymer (b) comprises: 90-95 mol % ofethylene; 5-10 mol % of alpha-olefin; and 0-2 mol % of a diene.
 13. Thecable of claim 1, wherein the alpha-olefin in the copolymer (b) is1-hexene or 1-octene.
 14. The cable of claim 1, wherein the crystallinepropylene homopolymer or copolymer (a) has a melting enthalpy greaterthan 75 J/g.
 15. The cable of claim 14, wherein the crystallinepropylene homopolymer or copolymer (a) has a melting enthalpy greaterthan 85 J/g.
 16. The cable of claim 1, wherein the copolymer (b) ispresent in admixture with the crystalline propylene homopolymer orcopolymer (a) in a predetermined amount, so as to make the resultingpolymer mixture sufficiently flexible.
 17. The cable of claim 16,wherein the copolymer (b) is present in admixture with the crystallinepropylene homopolymer or copolymer (a) in an amount such that theresulting polymer mixture has a elongation at break value, measuredaccording to CEI standard 20-34, §5.1, of at least 100%, and a 20%modulus value, measured according to CEI standard 20-34, §5.1, of lessthan 10 MPa.
 18. The cable of claim 17, wherein the copolymer (b) ispresent in admixture with the crystalline propylene homopolymer orcopolymer (a) in an amount such that the resulting polymer mixture has aelongation at break value, measured according to CEI standard 20-34,§5.1, of at least 200%, and a 20% modulus value, measured according toCEI standard 20-34, §5.1, of less than 7 MPa.
 19. The cable of claim 1,wherein the polymer mixture comprises from 10% to 60% by weight ofcrystalline propylene homopolymer or copolymer (a) and from 40% to 90%by weight of copolymer (b), the percentages being relative to the totalweight of the polymeric components (a) and (b).
 20. The cable of claim19, wherein the polymer mixture comprises from 15% to 50% by weight ofcrystalline propylene homopolymer or copolymer (a) and from 50% to 85%by weight of copolymer (b), the percentages being relative to the totalweight of the polymeric components (a) and (b).